The present invention relates to an ultrasonic transmitter-receiver to be used in a position detection apparatus or a distance measuring apparatus or the like for detecting the position or distance of an object by using ultrasonic waves.
A conventional ultrasonic transmitter will be described with reference to accompanying drawings. FIG. 34 is a side elevational view, in cross section, showing the construction of the conventional ultrasonic transmitter. In FIG. 34, a disc-shaped vibrating plate 342 made of a metal such as stainless steel is mounted with piezoelectric discs 340 and 341, one bonded to each face of the vibrating plate 342. The piezoelectric disc 341 is fixed to a base 346 by means of an elastic ring 343 which is a soft, elastic adhesive. A rod 345 for connecting a cone 344 thereto is provided on the vibrating plate 342 to which the other piezoelectric disc 340 is bonded.
As described above, the conventional ultrasonic transmitter is constructed with the piezoelectric discs 340, 341 sandwiching the vibrating plate 342 between them. The piezoelectric discs 340, 341 are arranged such that their polarizations are in the same direction. A bimorph vibration device 349 is thus constructed with the piezoelectric discs 340, 341 and the vibrating plate 342.
The cone 344, as a diaphragm held on the upper piezoelectric disc 340 via the rod 345, is a hollow conical structure made of a light metal such as aluminum. A vertex of the cone 344 is connected to one end of the rod 345, the other end of which is connected to the center of the vibrating plate 342. In this way, the bimorph vibration device 349 and the cone 344 are mechanically connected together.
In the conventional ultrasonic transmitter having the above-mentioned construction, the composite vibrating unit having the bimorph vibration device 349 and the cone 344 is constructed so that its resonant frequency coincides with a desired ultrasonic frequency. When an AC voltage is applied to the bimorph vibration device 349 in the composite vibrating unit causing the bimorph vibration device 349 to make deflective vibration, the composite vibrating unit makes vibration and an ultrasonic wave is output.
As shown in FIG. 34, the composite vibrating member consisting of the bimorph vibration device and the cone 344 is supported on the base 346 at a node of deflective vibration of the bimorph vibration device 349 via the elastic ring 343.
The conventional ultrasonic transmitter having the thus constructed bimorph vibration device is encased in a cylindrical housing 347 for enhanced protection against impact and dust. Terminal pins 348, 348' for applying a voltage to the piezoelectric discs 340, 341 and the vibrating plate 342 are provided passing through the base 346. The terminal pins 348, 348' are connected to the vibrating plate 342 and the piezoelectric discs 340, 341, respectively.
FIG. 35 is a perspective view showing the external appearance of the conventional ultrasonic transmitter provided with the housing 347. A protector 347a having a mesh structure is formed on the ultrasonic wave output side of the housing 347. The protector 347a is designed with care not to interfere with the output of ultrasonic waves.
Next, problems will be described that are encountered in the conventional ultrasonic transmitter having the above construction when increasing the sound-pressure of its output. FIG. 36 is a side view showing a vibrational displacement of an ideal cone 344a which is mounted on a piezoelectric vibrator, a bimorph vibration device, in order to increase the output of the ultrasonic sound-pressure. In FIG. 36, an alternate long and short dash line 360 indicates the stationary position of the cone 344a before the piezoelectric vibrator is excited into vibration, and a solid line 361 and a dashed line 362 respectively show the upper-end and lower-end positions of the ideal cone 344a when the piezoelectric vibrator is excited into vibration in an ideal condition. In FIG. 36, arrow A indicates the displacement direction of the deflective vibration of the piezoelectric vibrator. As shown in FIG. 36, the ideal cone 344a vibrates linearly in directions parallel to the displacement direction A of the deflective vibration.
To achieve increased output of ultrasonic sound-pressure, it is desirable that the cone 344a move linearly in reciprocating fashion in parallel with the displacement direction (the direction indicated by arrow A) of a deflective vibration of the piezoelectric vibrator by the deflective vibration of the piezoelectric vibrator. In actuality, however, the cone 344 does not move linearly in reciprocating fashion in parallel with the displacement direction of the deflective vibration when it makes vibration with a large amplitude. Possible causes are: the cone 344 is not made so as to be symmetrical about its conical center axis, or the cone 344 and the piezoelectric vibrator are not connected together precisely at their respective centers.
FIG. 37 is a side view showing one example of a vibrational displacement of a practical cone 344b when outputting an ultrasonic sound-pressure. As shown in FIG. 37, when actually outputting an ultrasonic sound-pressure, the deflective vibration of the piezoelectric vibrator is transmitted to the conical surface of the cone 344b and the cone 344b wobbles with its center axis swaying left and right. In FIG. 37, the left/right swaying motion is greatly exaggerated. As a result of the left/right sawing motion, the output of the sound-pressure of the cone 344b becomes smaller than its design value.
In FIG. 37, an alternate long and short dash line 370 indicates the position of the conical surface of the conventional cone 344b before the piezoelectric vibrator is excited into vibration, and solid line 371 and dashed line 372 respectively show the rightmost and leftmost positions of the conical surface of the cone 344b when the piezoelectric vibrator is excited into vibration. In FIG. 37, the direction indicated by arrow A is the displacement direction of the deflective vibration of the piezoelectric vibrator. As shown in FIG. 37, the rod 345 connecting the cone 344b to the piezoelectric vibrator receives bending moment forces very many times from directions other than the displacement direction of the deflective vibration (the direction indicated by arrow A). Therefore, the deflective vibration of the cone 344b cannot be made large in the displacement direction A. As a result, the rod 345 becomes fatigued, and its mechanical strength decreases, sometimes resulting in the breakage of the rod 345.
To prevent the rod 345 from breaking as described above, it has been practiced to increase the diameter of the rod 345 to increase the mechanical strength of the rod 345 against bending moment. Such construction, however, has lead to the problem that load for the deflective vibration of the piezoelectric vibrator increases, making it difficult to increase sound-pressure output.
Generally, an ultrasonic transmitter and an ultrasonic receiver are identical in construction. Accordingly, when deflective vibrations as described above occur in the ultrasonic receiver, the cone does not vibrate linearly along the designed deflection direction when an ultrasonic wave is received; this has lead to the problem that noise other than the received ultrasonic wave tends to occur and the receiving sensitivity to the incident ultrasonic wave tends to drop.
Next, a conventional ultrasonic transmitter, of which a horn is mounted on the above-described composite vibrating unit consisting of the piezoelectric vibrator and the cone, will be described with reference to drawings.
FIG. 38 is a side elevational view, in cross section, showing the construction of the conventional ultrasonic transmitter equipped with a horn.
The ultrasonic transmitter shown in FIG. 38 is constructed by mounting a conical-shaped horn 380 on the composite vibrating unit consisting of the bimorph vibration-device 349 and the cone 344 shown in FIG. 34. The cone 344, as a diaphragm held on the piezoelectric disc 340 via the rod 345, is a hollow conical structure made of a light metal such as aluminum. The vertex of the cone 344 is connected to one end of the rod 345, the other end of which is connected to the center of the vibrating plate 342. In this way, the bimorph vibration device 349 and the cone 344 are mechanically connected together.
In FIG. 38, reference numeral 381 indicates the position of the vibration node of the cone 344. The composite vibrating unit consisting of the bimorph vibration device 349 and the cone 344 is elastically connected to the base 346 at an open end of the cone 344 (the upper end of the cone 344 in FIG. 38) via an elastic ring 343 which is a soft adhesive. Accordingly, the piezoelectric discs 340, 341 and the electrode portions of the terminal pins 348 located inside the base 346 are protected against water drops and dust.
The ultrasonic transmitter shown in FIG. 38 has a soft and vibration absorbing material such as a sponge which is filled in the space enclosed by the bimorph vibration device 349 and the base 346, thereby preventing the vibration of the composite vibrating unit consisting of the bimorph vibration device 349 and the cone 344 from being transmitted to the base 346, while at the same time providing protection against mechanical shock.
In the conventional ultrasonic transmitter having the above construction, the horn 380 and the base 346 are connected together so that the center axis of the conical-shaped horn 380 coincides with the center axis of the cone 344.
As described above, in the conventional ultrasonic transmitter having the horn 380, the open end edge of the cone 344 is bonded to the base 346 using the elastic ring 343. As a result, when an AC voltage is applied to the bimorph vibration device 349, causing the bimorph vibration device 349 to make the deflective vibration, a vibration having a node 381 is set up on the conical surface of the cone 344. The ultrasonic wave emitted from the composite vibrating unit having the above-described structure propagates through the interior space of the conical-shaped horn 380 and is radiated into free space through a mouth 380a which is the opening of the horn 380.
Next, a description will be given of how the ultrasonic wave emitted from the inside surface of the cone 344 propagates inside the conical-shaped horn 380. FIG. 39 is a phase distribution curve diagram simulating the ultrasonic wave propagating inside the conical-shaped horn 380 in the conventional ultrasonic transmitter. In FIG. 39, reference numeral 393 indicates the center axis of the horn 380. Since the phase distribution of the ultrasonic wave is symmetrical between the right half and left half about the center axis 393 of the conical-shaped horn 380, the ultrasonic wave phase distribution curve diagram of FIG. 39 shows one half of the conical-shaped horn 380 divided along its center axis 393, and the right half is omitted.
In FIG. 39, the curved stripe patterns show in-phase propagation of the ultrasonic wave. A reference numeral 390 indicates the conical surface of the cone 344, a reference numeral 391 shows the inside surface of the conical-shaped horn 380, and a reference numeral 392 is an imaginary baffle assumed at the mouth 380a of the horn 380. In this simulation, vibrations other than those from the conical surface 390 of the cone 344 is excluded by the presence of the baffle 392.
As shown in FIG. 39, the phase of the ultrasonic wave propagating inside the conical-shaped horn 380 is disturbed near the conical surface 390 of the cone 344. However, if the horn length along the center axis of the horn 380 is sufficiently large, phase discontinuities of the ultrasonic wave, which are caused by displacements opposite in phase across the vibration node of the cone 344, appear in a region near the conical surface 391 of the horn 380 and in a distance from the center axis 393 of the conical-shaped horn 380. Near the center axis 393 of the conical-shaped horn 380, the ultrasonic wave have substantially the same phase in a plane perpendicular to the center axis 393 of the horn 380. The sound-pressure directivity pattern of the above conventional ultrasonic transmitter becomes narrow when the size of the opening of the mouth 380a of the horn 380 is increased, and becomes broad when the opening is reduced. In this way, in the conventional ultrasonic transmitter, the sound-pressure directivity has greatly depended on the size of the mouth 380a of the conical-shaped horn 380.
FIG. 40 is a diagram in a polar coordinate system. FIG. 40 shows the relationship between the angle relative to the center axis 393 of the horn 380 and the sound-pressure of the output ultrasonic wave, when observed at a point a given distance away from the mouth 380a of the conical-shaped horn 380 for the above-configured conventional ultrasonic transmitter having a long horn. Here, the frequency was 40 kHz, the horn length was 120 mm, and the distance from the mouth 380a to the observation point was 300 mm.
As shown in FIG. 40, the conventional ultrasonic transmitter achieves some degree of ultrasonic wave directivity by providing a large conical-shaped horn 380. This means that the provision of the large conical-shaped horn 380 was essential in the conventional ultrasonic transmitter if some degree of ultrasonic wave directivity was to be achieved.
Next, a conventional ultrasonic transmitter of a drip-proof type will be described with reference to drawings. FIG. 41 is a side elevational view, in cross section, showing the construction of the conventional drip-proof type ultrasonic transmitter.
The word "drip-proof" is used in the meaning as described in IEEE Standard Dictionary of Electrical and Electronics Terms (Fourth Edition) published by The Institute of Electrical and Electronics Engineers, Inc New York, N.Y. in 1998. That is "so constructed or protected that successful operation is not interfered with when falling drops of liquid or solid particles strike or enter the enclosure at any angle from 0 to 15 degrees from the downward vertical unless otherwise specified."
As shown in FIG. 41, the conventional drip-proof type ultrasonic transmitter comprises a piezoelectric disc 410, a disc-shaped piezoelectric element, which is attached to an inside face of the bottom of a bowl-shaped metal vibrating plate 411. Two terminal pins 413 and 414 are provided passing through a base 412 which is attached so as to close the opening of the metal vibrating plate 411. In the conventional drip-proof type ultrasonic transmitter, a conical face part 415 is formed in the upper part of the side portion of the metal vibrating plate 411, as shown in FIG. 41.
In FIG. 41, electrodes are formed on both principal faces, i.e., the upper and lower faces, of the piezoelectric disc 410, and the upper face of the piezoelectric disc 410 is fixed to the inside face of the metal vibrating plate 411 in electrically conducting relationship. The metal vibrating plate 411, to which the piezoelectric disc 410 is cemented, is made of a high rigidity metallic material such as stainless steel.
The terminal pin 413 is electrically connected to the metal vibrating plate 411, while the other terminal pin 414 is electrically connected to the electrode on the lower face of the piezoelectric disc 410. When an AC voltage of an ultrasonic frequency is applied to these terminal pins 413, 414, the piezoelectric disc 410 vibrates at the ultrasonic frequency; this vibration is transmitted to the metal vibrating plate 411, and thus the drip-proof type ultrasonic transmitter outputs an ultrasonic wave.
The thus constructed conventional drip-proof type ultrasonic transmitter has a hermetically sealed structure in which the piezoelectric disc 410 is enclosed by the metal vibrating plate 411 and the base 412. With this hermetically sealed structure, the electrode faces of the piezoelectric disc 410 are protected from the outside environment, and the drip-proof type ultrasonic transmitter is thus provided with a drip-proof capability.
FIG. 42 is a side elevational view, in cross section, conceptually showing the conventional drip-proof type ultrasonic transmitter in the condition of a vibrational displacement. The magnitude of the sound-pressure output of the drip-proof type ultrasonic transmitter is determined by the displacement volume (the volume that the deflected space displaces) of the vibrating portion of the metal vibrating plate 411 when it makes vibration. Accordingly, to increase the sound-pressure output of the drip-proof type ultrasonic transmitter, the amount of deflective displacement of the metal vibrating plate 411 must be made as large as possible.
In view of this, the conventional drip-proof type ultrasonic transmitter has been constructed so as to increase the amplitude of the face of the metal vibrating plate 411 to which the piezoelectric disc 410 is bonded, by forming the conical face part 415 in the upper part of the side portion of the metal vibrating plate 411, as shown in FIG. 41.
The conventional drip-proof type ultrasonic transmitter having the above construction has been manufactured by forming the metal vibrating plate, for example, by stamping, and by bonding the piezoelectric disc to the thus formed metal vibrating plate.
In the thus constructed conventional ultrasonic transmitter-receiver, the cone and the piezoelectric vibrator have had to be securely connected together precisely at a predetermined position, and in the case of the ultrasonic transmitter, it has not been possible to increase the sound-pressure output unless the two members are connected together precisely in position. In the case of the ultrasonic receiver, failing to do this has resulted in an ill effect on the receiving sensitivity.
Furthermore, to increase sound-pressure output or achieve sharp directivity in the conventional ultrasonic transmitter equipped with a horn, or to increase the receiver sensitivity in the conventional ultrasonic receiver equipped with a horn, it has been necessary to use a large-size horn, the resulting problem being that the conventional ultrasonic transmitter-receiver increase in size.
In the conventional drip-proof type ultrasonic transmitter to achieve a further increase in sound-pressure output, it has been necessary to further increase the area of the vibrating face. Also, to produce vibration at the desired ultrasonic frequency in the resonant mode of the above-described structure in order to obtain a large output, the thickness of the vibrating portion of the metal vibrating plate has had to be increased in accordance with an increase in the area of the vibrating portion.
Increasing the thickness of the vibrating portion of the metal vibrating plate, however, has involved the following problems:
(1) The rigidity of the vibrating portion increases, as a result of which the amount of deflective displacement cannot be made large; and PA1 (2) The metal vibrating plate cannot be manufactured by simple and inexpensive metal forming means such as stamping. PA1 a piezoelectric vibrating member having electrodes to be supplied with or outputting therefrom a signal of an ultrasonic frequency; and PA1 a diaphragm having a cone of a hollow conical structure, the cone having a node of vibration at positions symmetrical about a center axis thereof and a substantial conical vertex of the cone is connected to a center of vibration of the piezoelectric vibrating member. PA1 a piezoelectric vibrating member having electrodes to be supplied with or outputting therefrom a signal of an ultrasonic frequency; PA1 a diaphragm having a cone of a hollow conical structure, the cone having a node of vibration at positions symmetrical about a center axis thereof and a substantial conical vertex of the cone is connected to a center of vibration of the piezoelectric vibrating member, the piezoelectric vibrating member and the diaphragm together constituting a composite vibrating unit; PA1 a housing, separated by a predetermined distance from an open end edge of a conical base of the cone, accommodating therein a composite vibrating unit, and elastically supporting the piezoelectric vibrating member thereon; and PA1 a film member, provided in such a manner as to connect between the open end edge of the cone and the housing, for applying substantially uniform tension in radial directions around the center axis of the cone PA1 a piezoelectric element having electrodes to be supplied with or outputting therefrom a signal of an ultrasonic frequency; PA1 a vibrating cylinder which has a cylindrical structure closed with an upper base wall at one end and opened at the other end, wherein the piezoelectric element is fixedly attached to the upper base wall and a portion surrounding a portion where the piezoelectric element is fixedly attached is formed thinner than the portion where the piezoelectric element is fixedly attached; PA1 a base for closing the open end of the vibrating cylinder; and PA1 terminals provided passing through the base and electrically connected to the electrodes of the piezoelectric element. PA1 a piezoelectric vibrating member having electrodes to be supplied with or outputting therefrom a signal of an ultrasonic frequency; PA1 a diaphragm having a cone of a hollow conical structure, and connected to a center of vibration of the piezoelectric vibrating member at a substantial conical vertex of the cone, and the piezoelectric vibrating member and the diaphragm together constituting a composite vibrating unit; PA1 a housing, forming an opening separated by a predetermined distance from an open end edge of a conical base of the cone, accommodating therein a composite vibrating unit, and elastically supporting the piezoelectric vibrating member thereon. PA1 a piezoelectric vibrating member having electrodes for outputting therefrom a signal of an ultrasonic frequency; PA1 a diaphragm having a cone of a hollow conical structure, the cone having a node of vibration at positions symmetrical about a center axis thereof and a substantial conical vertex of the cone is connected to a center of vibration of the piezoelectric vibrating member, the piezoelectric vibrating member and the diaphragm together constituting a composite vibrating unit; PA1 a housing, forming an opening separated by a predetermined distance from an open end edge of a conical base of the cone, accommodating therein the composite vibrating unit, and elastically supporting the piezoelectric vibrating member thereon; and PA1 a horn whose throat is connected to the opening of the housing, the horn forming a space spreading from the opening toward a distal end. PA1 a piezoelectric vibrating member having electrodes for outputting therefrom a signal of an ultrasonic frequency; PA1 a diaphragm having a cone of a hollow conical structure, the cone having a node of vibration at positions symmetrical about a center axis thereof and a substantial conical vertex of the cone is connected to a center of vibration of the piezoelectric vibrating member: and PA1 a base for elastically supporting thereon a composite vibrating unit having the piezoelectric vibrating member and the diaphragm, and wherein: PA1 the distance from the open end edge of the cone to the composite vibrating unit, measured in a direction parallel to the center axis of the cone, is equal to an integral multiple of the wavelength of an output ultrasonic wave. PA1 a piezoelectric vibrating member having electrodes for outputting therefrom a signal of an ultrasonic frequency; PA1 a diaphragm having a cone of a hollow conical structure, wherein a substantial conical vertex of the cone having a node of vibration at positions symmetrical about a center axis thereof is connected to a center of vibration of the piezoelectric vibrating member; and PA1 a base for elastically supporting thereon a composite vibrating unit having the piezoelectric vibrating member and the diaphragm, and wherein: PA1 the distance from the open end edge of the cone to an upper face of the base, measured along a perpendicular dropped from the upper face to the open end edge, is equal to an integral multiple of the wavelength of an output ultrasonic wave.
The present invention resolves the above-enumerated problems of the conventional ultrasonic transmitter, and it is an object of the present invention to provide an ultrasonic transmitter-receiver capable of producing large sound-pressure output, or an ultrasonic receiver capable of increasing receiving sensitivity.
It is another object of the present invention to provide an ultrasonic transmitter achieving a large sound-pressure output and sharp directivity with a small-size horn, or an ultrasonic receiver achieving sharp directivity with a small-size horn.
It is a further object of the present invention to provide a drip-proof type ultrasonic transmitter capable of producing large sound-pressure output, a drip-proof type ultrasonic receiver having a high receiving sensitivity.